1. Field of the Invention
The present invention relates to a lithium secondary battery. More particularly, the present invention relates to a lithium secondary battery, in which a fixing unit for fixing a terminal plate to an electrode terminal is provided in the terminal plate in order to prevent the terminal plate from rotating when an electrode tap is welded to a cap assembly or when the cap assembly is assembled with an upper portion of a can.
In addition, the present invention relates to a lithium secondary battery, in which an anti-rotation unit is provided in a cap plate to prevent an electrode terminal from rotating.
Furthermore, the present invention relates to a lithium secondary battery, in which an anti-rotation unit is provided in an electrode terminal to prevent the electrode terminal from rotating.
2. Description of the Related Art
Recently, light-weight portable wireless appliances, such as video cameras, potable phones and potable computers, have been fabricated with various functions, so studies have been actively performed in relation to secondary batteries used as power sources for these portable wireless appliances. For instance, the secondary batteries include Ni—Cd batteries, Ni-MH batteries, Ni—Zn batteries and lithium secondary batteries. Among other things, lithium secondary batteries are rechargeable batteries, which can be fabricated in a compact size with a high capacity. Lithium secondary batteries have a high operational voltage and high energy density per unit weight and accordingly, lithium secondary batteries are extensively used in advanced electronic technology fields.
A lithium secondary battery can be fabricated by accommodating an electrode assembly including a first electrode plate, a second electrode plate and a separator in a can together with an electrolyte, and then sealing an upper opening of the can by using a cap assembly. In general, the first electrode plate is a negative electrode plate and the second electrode plate is a positive electrode plate.
The cap assembly includes a cap plate, an insulating plate, a terminal plate and an electrode terminal. The cap assembly is accommodated in an insulating case and assembled with the upper opening of the can, thereby sealing the can.
The cap plate is made of a metal plate having a size and a shape corresponding to those of the upper opening of the can. The cap plate has a first terminal hole formed at the center thereof and the electrode terminal is inserted into the first terminal hole. When the electrode terminal is inserted into the first terminal hole, a gasket tube is provided around the electrode terminal in order to insulate the electrode terminal from the cap plate. In addition, an electrolyte injection hole is formed on one side of the cap plate. After the cap assembly has been assembled with the upper opening of the can, the electrolyte is injected into the can through the electrolyte injection hole. Then, the electrolyte injection hole is sealed by a plug.
The electrode terminal is connected to a first electrode tap of the first electrode plate or a second electrode tap of the second electrode plate so that the electrode terminal serves as either a negative electrode terminal or a positive electrode terminal.
The insulating plate is made of an insulating material identical to the material for the gasket tube and is attached the lower surface of the cap plate. The insulating plate has a second terminal hole, which is aligned to correspond to the first terminal hole of the cap plate and into which the electrode terminal is inserted. The insulating plate is formed on the lower surface thereof with a recess having a size and a shape corresponding to those of the terminal plate such that the terminal plate can be arranged in the recess.
The terminal plate is made of a Ni alloy and is attached to the lower surface of the insulating plate. The terminal plate is formed with a third terminal hole, which is aligned to correspond to the first terminal hole of the cap plate and into which the electrode terminal is inserted. Since the electrode terminal inserted into the first terminal hole of the cap plate is insulated from the terminal plate by the gasket tube, the terminal plate can be electrically connected to the electrode terminal while being electrically insulated from the cap plate.
After the electrode terminal has been inserted into the terminal plate, a pressing force is applied to the electrode terminal from a lower portion of the terminal plate in order to rivet the electrode terminal to the terminal plate. Since the electrode terminal is fixed, the terminal plate and the insulating plate are also fixed by the electrode terminal.
However, since the terminal plate and the insulating plate are fixed by the electrode terminal having a cylindrical structure, there is a possibility that the terminal plate and the insulating plate can rotate about the electrode terminal. In particular, if the fixing force of the electrode terminal is relatively small, the possibility may increase.
In addition, when the first electrode tap or the second electrode tap of the electrode assembly is welded to the terminal plate after the terminal plate has been assembled with the cap assembly, the terminal plate can rotate.
Furthermore, the terminal plate can rotate together with the insulating plate when cap assembly accommodated in the insulating case is assembled with the upper portion of the can.
If the first electrode tap of the lithium secondary battery is directly connected to a lower surface of the electrode terminal, the electrode terminal can rotate when it is assembled with the cap assembly. The electrode terminal can rotatably move the negative electrode tap electrically connected to the lower surface of the electrode terminal, thereby causing a short circuit between the can and the second electrode tap.
In addition, if the coupling force between the electrode terminal and the gasket tube or between the gasket tube and the terminal holes is insufficient, the cap assembly can rotate during the fabrication process for the secondary battery. The negative electrode tap electrically connected to the lower surface of the electrode terminal can rotatably move, thereby causing a short circuit with the can.